README
1Image::Pngslimmer version 0.30
2=============================
3
4OVERVIEW
5
6Image::Pngslimmer reduces the size of PNGs by removing non-critcal chunks and
7recompressing, filtering or palettizing images.
8
9Other tools, such as pngcrush (http://pmt.sourceforge.net/pngcrush/)
10will deliver better results for static PNGs and Image::Pnglimmer
11was orginally designed for dynamically created PNGs.
12
13use Image::Pngslimmer
14
15Image::Pngslimmer::ispng($blob) - returns 1 if the BLOB conforms to the
16structure for a PNG and that all CRCs are correct.
17
18Image::Pngslimmer::discard_noncritical($blob) - returns a BLOB stripped of any
19non-critcal chunks. If the passed-in BLOB does not conform to the basic
20structure of a PNG the returned BLOB is identical to the passed-in BLOB.
21The passed in BLOB is not altered by this function.
22
23Image::Pngslimmer::analyze($blob) - after calling Image::Pngslimmer::ispng($blob)
24this will iterate through the chunks in the supplied byte stream represented by
25$blob and return an array of strings describing the chunks in the PNG. It can be
26useful for testing the "before and after" effect of discard_noncritical($blob).
27
28Image::Pngzlimmer::zlibshrink($blob) will attempt to improve compression of the
29supplied BLOB.
30
31Image::Pngslimmer::filter($blob) will attempt to apply adaptive filtering for
32better compression of the supplied BLOB - filtering normally results in better
33compression once zlibshrink() is reapplied if the original image is truecolour.
34
35Image::Pngslimmer::indexcolours($blob) will attempt to losslessly convert the
36supplied PNG to a colour indexed image - of the image contains more than 256
37colours this will not work and the original PNG is returned instead.
38
39Image::Pngslimmer::palettize($blob[, $colours[, $dither]]) will colour index
40(with a PLTE chunk) a 24 bit RGB image. If the original image has 256
41colours or less it will do this losslessly by calling indexcolours(), otherwise
42it will generate a palette by using the median cut algorithm. The size of the
43palette can be set by the optional $colours in the range 1 - 256 (the defult 0
44gives 256 colours). If the optional $dither is set to 1, then the output image
45will be dithered.
46
47Dithering is now up to 75 (!) times faster than in previous versions though
48still 3 - 5 times slower than simple quantization for most images.
49
50NB: Alpha channels in the original image will be lost with with quantization
51or indexation.
52
53
54Image::Pngslimmer::reportcolours($blob) will print details of the colour
55frequencies in the passed in PNG.
56
57
58INSTALLATION
59
60To install this module type the following:
61
62 perl Makefile.PL
63 make
64 make test
65 make install
66
67DEPENDENCIES
68
69
70POSIX
71Compress::Zlib
72Compress::Raw::Zlib
73
74
75COPYRIGHT AND LICENCE
76
77
78Copyright (C) 2006, 2007, 2008 by Adrian McMenamin
79<adrian AT mcmen DOT demon DOT co DOT uk>
80
81This library is free software; you can redistribute it and/or modify
82it under the same terms as Perl itself, either Perl version 5.8.4 or,
83at your option, any later version of Perl 5 you may have available.
84